T&T: "Then, once the motor is started, I switch to BOTH in order to charge"

[Faure, Marin]

>Marins statement in the above title on his Grand Banks may not apply as
he probably has a diode splitter in the charging system.

Actually, I did not make the statement in the subject line.  That was
made by the original poster.  We switch our battery selector to "All"
BEFORE we start the engines.  While battery selector switches have been
made for years and years with a "make before break" action, older
selector switches may not have been built this way.  If the current is
momentarily interrupted when changing the switch position with one of
these old-style switches and the engines are running, it can damage the
alternators.  The selector switch on our 1973 boat acts like a
make-before-break switch judging by the behavior of the lights when we
move the switch, but the switch does have a big warning on it not to
change positions while the engines are running, so we don't.

Our boat has its stock, very simple electrical system, and it does not
have splitters. according to the schematic.  Unless the battery selector
switch is in "All" the port alternator charges the port battery and the
starboard alternator charges the starboard battery.  Putting the battery
selector switch in "All" will connect both alternators to both
batteries.  We do this when running so that if we use the inverter for
something--- powering the microwave, for example--- both alternators
will put a charge into the port battery which is the one we've
designated "house" power and has the inverter connected to it.
Otherwise, only the port alternator (a stock 45 or 50 amp Motorola)
would be picking up the load of the microwave while the starboard
alternator contributed nothing. Likewise having the selector switch in
"All" means both alternators will be picking up the load of the anchor
windlass, which can be as much as 100 amps.  The alternators are fitted
with different size drive pulleys.  The starboard alternator spins
faster, and so picks up the "normal" load of instruments, lights, etc.
while the port alternator puts out no (or very little) current.  But
when the load exceeds a certain point---- after a day or two at anchor
or if the microwave, coffee maker, etc. is turned on using the
inverter--- both alternators share the load equally.  You can watch all
this happen on the ammeters.

______________________________
C. Marin Faure
GB36-403 "La Perouse"
Bellingham, Washington